Sequential Saturating Reactions of ZrCl₄ and H₂O Vapors in the Modification of Silica and γ-Alumina with ZrO₂

Abstract

Zirconia-modified silica and alumina samples were prepared by the atomic layer epitaxy technique using successive saturating reactions of ZrCl4 and H2O vapors. The growth of ZrO2 was followed by X-ray diffraction, diffuse reflectance IR Fourier transform spectroscopy, and 1H magic angle spinning NMR measurements. In addition, coverage of the silica surface was estimated by low-energy ion scattering (LEIS). At the reaction temperature of 300 °C the main reaction of ZrCl4, on both supports, occurred with surface OH groups, leading to amorphous ZrCl x species. In addition, part of the molecules reacted to form ZrO2 agglomerates while simultaneously chlorinating OH groups of the supports. Water treatment removed Cl from the ZrCl x surface species, leaving behind Zr−OH groups, and released the directly chlorinated OH groups. Both the reappearing OH groups of the support and the Zr−OH groups were then again available during the next ZrCl4 treatment for both main reactions of ZrCl4. As the reaction cycles were repeated the concentration of amorphous Zr in the samples increased together with the amount of crystalline ZrO2 and surface coverage. On silica, after five cycles of repeated reactions when an average surface density of 5 Zr/nm2 had been achieved, 25% of the original accessible OH groups were still present on the surface. At that point, LEIS measurements showed 50% coverage. On the surface of both silica and alumina, ZrO x was present in the form of tetragonal agglomerates and an amorphous network phase. Two types of Zr−OH groups were identified.

Supported Tantalum Oxide and Supported Vanadia-tantala Mixed Oxides: Structural Characterization and Surface Properties

“…The actual deposition process is discussed in detail in earlier publications. [21][22][23][24][25][28][29][30] Pyridine adsorption was performed after calcination of the samples at 500°C for 16h, and subsequent degassing at 150°C for 3 h. The samples were exposed to pyridine vapor for 30 min. After evacuation for 3 h at 150°C, the FTIR-PAS spectra were recorded.…”

Formation of Metal Oxide Particles in Atomic Layer Deposition During the Chemisorption of Metal Chlorides: A Review

“…[9,10] Ti(OH) m Cl 4±m is likely to represent relatively stable intermediates, as large TiO 2 crystals form in the saturating reaction of TiCl 4 with porous silica. [8] As examples of stable oxychlorides, TaOCl 3 and NbOCl 3 can be mentioned; these are transported, unreacted, out of the reactor during ALD processing.…”

“…Compared to the TiO 2 particles observed on high surface area substrates, the ZrO 2 particles were considerably smaller, with dimensions in the order of 10 nm. [10] Kytökivi et al [9] suggested that the ZrO 2 particles could originate from the formation and decomposition of hydroxychloride Zr(OH) m Cl 4±m or oxychloride ZrOCl 2 intermediates. Kytö-kivi and Haukka [11] showed, by infrared measurements, that the TiO 2 and ZrO 2 particles are bonded to the silica substrate through Si±O±Ti and Si±O±Zr bonds, respectively.…”

Low-Temperature Deposition of Zirconium Oxide-Based Nanocrystalline Films by Alternate Supply of Zr[OC(CH3)3]4 and H2O

“…With no evidence of the monoclinic phase, nanocrystalline tetragonal ZrO 2 could be obtained in non-doped ultrathin ZrO 2 layers, 5±15 nm thick or below. [17,18] Films of monoclinic ZrO 2 had permittivity values of 20, while the nanolaminates, consisting of amorphous Ta 2 O 5 and tetragonal ZrO 2 , had a permittivity value as high as 33. [17] To date, no reports have been published on the application of alkoxide or metal±organic Zr precursors in the ALD process.…”